Ossification of ulna
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The ulna is ossified from three centers: one each for the body, the inferior extremity, and the top of the olecranon.
Ossification begins near the middle of the body, about the eighth week of fetal life, and soon extends through the greater part of the bone.
At birth the ends are cartilaginous.
About the fourth year, a center appears in the middle of the head, and soon extends into the styloid process.
About the tenth year, a center appears in the olecranon near its extremity, the chief part of this process being formed by an upward extension of the body.
The upper epiphysis joins the body about the sixteenth, the lower about the twentieth year.
